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Rates of Reaction

What is Calorimetry?

Measuring the change in energy of a chemical reaction
is called calorimetry. A simple method for measuring
the amount of energy given out by a fuel is shown below.

What is a Calorimeter?

The apparatus used to measure the change in energy is called
a calorimeter. A known amount of water is placed in a glass
or copper container. Burning a fuel is an exothermic reaction.
The amount of energy released can be calculated from
the increase in temperature of the water as the fuel burns.

The simple calorimeter shown above

The calorimeter does not collect all of the heat released
from burning the fuel because some heat is lost to the
surroundings. The amount of heat lost can be minimised
by using a lid on top of the calorimeter and by
putting a draught excluder all around it but some heat
is always lost and so this is not a good method to
find the maximum amount of heat available from a fuel.

The calorimeter is easy to make and use. The calorimeter
is made from copper which is an excellent conductor
of heat. The copper allows the heat released from burning
the fuel to be conducted efficiently to the water.

If the experiment is repeated using different fuels, the
amount of heat lost by the calorimeter is similar in
each case and so this is a good method for comparing
the amount of heat released from different fuels.

To make the comparison fair, the variables to be kept constant are

1. the amount of water in the calorimeter.

2. the starting temperature of the water.

3. the increase in temperature of the water.

4. the distance between the burner and the calorimeter.

The picture below shows a different type of calorimeter
that can be used for a chemical reaction in a solution.

An insulated container with a thermometer inside is used to
measure the temperature change during the reaction.
This type of calorimeter can be used for neutralisation reactions.

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